package bus

import "sync"

type EventChan chan Event

var _ Publisher = (*Bus)(nil)
var _ Subscriber = (*Bus)(nil)

type Bus struct {
	subscribers map[string][]EventChan
	rm          sync.RWMutex
}

func New() *Bus {
	return &Bus{
		subscribers: make(map[string][]EventChan, 0),
	}
}

func (bus *Bus) Subscribe(topic string, ch EventChan) {
	bus.rm.Lock()
	defer bus.rm.Unlock()
	if prev, found := bus.subscribers[topic]; found {
		bus.subscribers[topic] = append(prev, ch)
	} else {
		bus.subscribers[topic] = append([]EventChan{}, ch)
	}
}

func (bus *Bus) UnSubscribe(topic string, ch EventChan) {
	bus.rm.Lock()
	defer bus.rm.Unlock()
	channels, found := bus.subscribers[topic]
	if !found {
		return
	}
	for i, c := range channels {
		if c == ch {
			channels = append(channels[:i], channels[i+1:]...)
		}
	}
}

func (bus *Bus) Start() error {
	return nil
}

func (bus *Bus) Stop() {
}

func (bus *Bus) Publish(topic string, ev Event) {
	bus.rm.RLock()
	defer bus.rm.RUnlock()
	ch, found := bus.subscribers[topic]
	if !found {
		return
	}
	channels := append([]EventChan{}, ch...)
	go func(ev Event, channel []EventChan) {
		for _, ch1 := range channel {
			ch1 <- ev
		}
	}(ev, channels)
}